Swivels are very important in connection, for example, with floating production units. Failure, leakage, etc. in a swivel result in a stoppage of production from parts of or the whole field. The operators therefore take great pains to ensure that a swivel has double seals and that, in the event of leakage of one or more of the seals, it is possible to repair/reduce the leakage without having to completely close down production. There are solutions in the prior art where a spare seal is mounted on the actual swivel, and where it can be installed without dismantling the whole swivel. In these cases, however, the swivels are of a relatively large size and this kind of solution is not suitable, for example, for more compact multi-channel swivels. In our opinion, therefore, this is a solution that is not good enough and is not applicable for all types of swivel.
Leakage of a seal, for example, internally in a swivel can have highly dramatic consequences. Seal leakage may have many causes, such as material failure in seals, defects in the sealing surfaces, typically involving scaling, scratches, wear, etc., puncture of the seal or extrusion of the seal. It is very difficult to safeguard entirely against such causes. An active quality assurance program, extended testing of materials and complete systems are ways to improve the situation, but they do not entirely eliminate the chances of unforeseen error.
In many types of swivels there are barrier-activated seals. This means that the dynamic and the static seals in a swivel can be activated by means of a barrier oil, where the pressure of the barrier oil is always higher than the pressure in the main swivel channel. If a leakage occurs over a seal, this will result in consumption of barrier oil, and this is recorded in control systems so that excessive consumption of the oil triggers an alarm. The operator is therefore made aware that there is consumption of barrier oil and can identify which seal is leaking.
If the leak over the seal is too big, the operator can either choose to continue on the secondary seal or repair the damaged seal. Generally it is undesirable to continue production only on a secondary seal and it takes an unduly long time to dismantle a swivel and replace the damaged seal. This is also expensive since during this period the production being carried out through the swivel has to be closed down. It is therefore desirable to achieve a sealing system that solves this problem while at the same time providing a solution for how the existing damaged seal can be repaired in a very simple manner.
An object of the present invention is to solve the above-mentioned problem and/or improve the situation. It is also an object to provide a solution that can be employed on most types of barrier-activated seals, particularly for barrier-activated seals in swivels used in the oil industry. It is also an object to provide a sealing system that is useful, easy to use and monitor and does not require the whole swivel to be dismantled in order to achieve repair/improvement of the seal. It is also an object to provide a solution where the primary seal in the seal series can continue to be used, even when it is damaged and leaking on account of this.
A sealing device, an improved sealing device and a method are provided that fulfil the above-mentioned objects.